I. Field
The following description relates generally to wireless communications and more particularly to reestablishment procedures in a wireless communications environment.
II. Background
Wireless communication systems are widely deployed to provide various types of communication content, such as voice, data, video, and so forth, and to communicate information regardless of where a user is located (e.g., inside or outside a structure) and whether a user is stationary or moving (e.g., in a vehicle, walking). These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available systems resources (e.g., bandwidth and transmit power). Multiple-access systems include Frequency Division Multiple Access (FDMA) systems, Time Division Multiple Access (TDMA) systems, Code Division Multiple Access (CDMA) systems, Orthogonal Frequency Division Multiple Access (OFDMA) systems, Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) systems, and others.
Generally, wireless multiple-access communication systems can simultaneously support communication for multiple mobile devices. Each mobile device can communicate with one or more base stations through transmissions on forward and reverse links. The forward link (or downlink) refers to the communication link from base stations to mobile devices. The reverse link (or uplink) refers to the communication link from mobile devices to base stations. These communication links can be established through single-input-single-output (SISO) systems, multiple-input-single-output (MISO) systems, multiple-input-multiple-output (MIMO) systems, and so forth. In addition, mobile devices can communicate with other mobile devices (and/or base stations with other base stations) in peer-to-peer wireless network configurations.
If a radio link failure occurs, a mobile device is configured to perform reestablishment procedures. A purpose of reestablishment procedures is to reestablish a connection, such as an RRC (Radio Resource Control) connection, which involves resumption of SRB1 (Signaling Radio Bearer 1) and reactivation of security. A mobile device can initiate a reestablishment procedure when there is detection of a radio link failure, when there is a handover failure, when there is a mobility from E-UTRA (Evolved UMTS (Universal Mobile Telecommunications System) Terrestrial Radio Access (E-UTRA)) failure, when there is an integrity check failure, and/or when there is a RRC connection reconfiguration failure. Once the reestablishment procedure is initiated, mobile device is required to perform cell selection to obtain service. According to traditional procedures, mobile device can only select a suitable E-UTRA cell for reestablishment. The traditional procedures are acceptable when there is no emergency call. However, when there is an emergency call, mobile device might encounter the situation where no suitable E-UTRA cell is present, but there is an acceptable E-UTRA cell (which is a cell where mobile device can obtain emergency services (only)). Based on the traditional procedures, mobile device will ignore the acceptable E-UTRA cell. Therefore, since mobile device finds no cell on which reestablishment is allowed, mobile device goes to idle mode and the call needs to be reinitiated by the mobile device user, which is an undesirable result in the case of an emergency call.
If an acceptable cell is the only cell available to mobile device, the delay before mobile device enters idle mode can be significant. In the case of a mobile device that supports multiple Radio Access Technologies (RATs), there is the possibility that mobile device is able to find some service on the other RAT. However, searching all frequencies of all RATs may take a long time in the case of a mobile device supporting many technologies. Even in the case of an “LTE only” mobile device, the mobile device will continue to search for any suitable E-UTRA cell until a reestablishment timer (such as T311) expires. In an example, a maximum value of a reestablishment timer can be about 30 seconds, which, in an emergency situation, can be an extremely long time.